This invention relates to a thin magnetic metal film type recording medium and, more particularly, to an improvement in a protective film employed therein.
As a magnetic tape, such as an audio tape or a video tape, a so-called coated magnetic recording medium, produced by application of a magnetic paint on a non-magnetic recording medium followed by drying in situ, is in extensive use. The magnetic paint, in turn, is produced by dispersing powdered magnetic materials, such as powders of magnetic oxides or alloys, and an organic binder, in an organic solvent, and kneading the resulting product.
On the other hand, with increasing demand for high density magnetic recording, a so-called thin magnetic metal film type magnetic recording medium, in which a magnetic layer is formed by directly depositing a magnetic metal material, such as Co--Ni alloys, Co--Cr alloys or Co--O on a non-magnetic substrate by plating or vacuum thin-film forming means, such as vacuum deposition, sputtering or ion plating, has been proposed and attracted attention.
The thin magnetic metal film type magnetic recording medium suffers from recording demagnetization or loss in thickness on reproduction to a significantly lesser extent and is superior in electro-magnetic conversion properties for short wavelengths since it is superior in coercivity and rectangular ratio and its magnetic layer can be reduced in thickness. In addition, since there is no necessity of mixing the binder as a non-magnetic material in the magnetic layer, it is possible to raise packing density of the magnetic material. Thus there is a favorable prospect for the thin magnetic metal film type magnetic recording medium as a recording medium for high density magnetic recording due to its ascendancy in magnetic properties.
In particular, an oblique deposition type magnetic recording medium, in which a magnetic layer has been formed by vacuum depositing a magnetic metal material from an oblique direction has already been put to practical use since it is superior in electro-magnetic conversion characteristics and is capable of producing a higher playback output.
The thin magnetic metal film type magnetic recording medium, thus produced by forming a thin magnetic metal film as a magnetic layer on a non-magnetic substrate, is usually provided further with a carbon protective layer, a lubricant or a rust-proofing agent on the magnetic layer for producing durability, good running performance and preservability. Of these, the lubricant and the rust-proofing agent are provided by dissolving these in respective solvents to produce a lubricant paint and a paint of the rust-proofing agent and top-coating the respective paints on the surface of the protective layer by a dipping method.
However, the lubricant or the rust-proofing agent, thus top-coated on the surface of the underlaying layer, tends to be lost due to sliding contact with various sliding components, such that lubricating and rust-proofing properties cannot be maintained without difficulties for prolonged tome on the recording medium. In addition, if the rust-proofing material, mainly employed for preventing rusting of the thin magnetic metal film, is top-coated on the protective layer, it is not directly contacted with the thin magnetic metal layer, so that it is unable to prohibit rusting of the magnetic metal film satisfactorily.